A conventional drive line coupling or constant velocity universal joint ("U-joint") is a linkage that transmits rotation between two shafts whose axes are coplanar but not coinciding. The conventional U-joint finds applications in almost every class of machinery, such as automobiles, trucks, farm machinery, industrial equipment, boats, ships, airplanes and helicopters.
The most common U-joint is a Cardan joint. It consists of two yokes attached to their respective shafts (an input drive shaft and an output drive shaft) and connected by means of a cross journal assembly. Bearings are mounted between the yokes and the cross journal to facilitate torsional transmission between the shafts and enable the shafts to be angularly displaced relative to one another.
An angle of up to approximately 35.degree. may be formed between the input drive shaft and the output drive shaft, if the rotational velocity of the drive line is not excessive when the angle is large. The higher the rotational velocity the smaller the angle which can be formed between the shafts. The output drive shaft makes one revolution for each revolution of the input drive shaft.
Experience has shown that conventional U-joints have a fairly high rate of failure. A significant number of these failures are related to lubricating film breakdown. This may be caused by a lack of lubricant, inadequate lube quality for the application, inadequate initial lubrication, or failure to lubricate properly and often enough. Other failures have been associated with installation and manufacturing errors as well as excessive angular displacement between the shafts and excessive operational speeds. Drive shaft failures through torque, fatigue and bending are associated with overload, excessively high U-joint angles and drive shaft lengths excessive for operating speeds. Vibrations caused by slight variation in the RPM (revolutions per minute) of the output drive shaft relative to the input drive shaft (resulting from the centers of the angular rotation of the coupling being rigidly held in one rotating plane) are also a major source of failure in conventional U-joints. These vibrations over time wear out the bearings and ultimately lead to failure of the joint. They also make for rough and noisy operation.
The present invention is directed to overcoming or at least minimizing some of the problems mentioned above.